This invention is related to a process for obtaining improved structure build-up of baked products as well as new dextrans and new micro-organisms producing them. The present invention is also related to dough and baked products containing these dextrans.
The rheological properties of a dough are determinant for the quality of the baked end product. In order to estimate the quality of bread and baked products in general, the parameters listed hereafter are used: volume, crumb structure softness and shelf life, color of the crumb and the crust, flavor and shape (round, flat).
So called bread improvers are used to enhance the rheological properties of the dough and consequently, to obtain a better baked end product. For this purpose, chemical agents are used, such as: potassium bromate, ascorbic acid, iodates, azodicarbonamide, cysteine. Emulsifiers are used too, such as: diacetyltartaric acid esters, sodium and calcium stearoyllactylate, and if necessary sucrose-esters.
Some enzymes also improve the properties of the dough. The usage of xcex1-amylases and xylanases is now widely spread. There are also oxidases and peroxidases which have a marginal, improving influence on the rheology of the dough, but this does not always means a better end product.
The use of polysaccharides as bread improvers is known and documented. The positive effect on dough rheology and on the total bread quality is always limited to specific cases or to combinations with other additives or ingredients. In most cases, guar gum is used, or locust bean gum, and if necessary carrageen or alginates (Ward F., 1993).
In practice, it is always by combining several of the above mentioned components that a commercial bread improver is created. The formulation of such a bread improver is adapted, according to the type of the end product, bread, rolls, or xe2x80x9cBelgian pistoletxe2x80x9d, xe2x80x9cFrench baguettexe2x80x9d, or according to the applied process: direct processing, retarded fermentation, deep frozen dough.
Although the possible combinations are endless, it is clear that the current additives and ingredients do not always meet the strict requirements of the modern bakery technology. Moreover, the use of certain additives is limited or prohibited by law. For instance, the use of bromate is forbidden in Europe, whereas it is limited in the U.S., on a voluntary basis. New ingredients which can replace existing chemical additives, or which have a new function, besides the currently existing additives are still being researched. Especially when they are based on natural products.
The ingredients mentioned above, and the additives for breads and rolls, are also used in pastry products. (cake, biscuit). In these pastry products, the volume of the baked end product is also one of the quality criteria besides, amongst others, softness and shelf life.
The use of dextrans in the field of bakery is not widely spread, although a number of applications have been described. The addition of dextrans in wheat doughs and the negative influence of this addition on the end quality of baked bread is known (Ross A. S. et al., J. Sci. Food Agric. 1992, 91-98; Ross A. S.: PhD Thesis, University of New South Wales (Australia), 1994 (XP000610156) and Dissertation Abstracts International, part 56, Nr. 7, p. 3524, 1996).
On the other hand, the Japanese patent application JP-07055124B2, the positive influence of dextrans on the softness and the shelf life of baked products has been proved. In addition, dextrans seem to have a small influence on the gassing power by yeast. This influence is comparable to other components such as locust bean gum, arabic gum, egg white, gelatine (Kolostori M., Elelmezesi Ipar 1978, 32(3), 107-112).
The U.S. Pat. No. 2,983,613 describes incorporating into the dough an amount of dextrans sufficient to soften the gluten content of the dough and to increase the specific volume of the resultant bakery product. This document describes that the bread which contains dextrans was about 20% greater in volume than products which do not contain dextrans.
Said dextrans are prepared by growing the micro-organism Leuconostoc mesenteroides B512, resulting in dextrans having a molecular weight from about 2xc3x97106 to about 4xc3x97106 dalton.
Dextrans have been described in EP-0153 013-A as bulking agent in formulations, suitable for enteral administration to man. This is mainly for diet reasons (low calorie) and for the treatment of a condition of the gastrointestinal tract in a human.
Dextrans can be synthesized by bacteria. Dextrans are xcex1-D-glucans, which are mainly composed of (1-6) linked xcex1-D-glucopyranosyl residues) They are mainly produced by bacteria which grow on a substrate, the only source of carbon being sucrose. These bacteria mainly belong to the group of lactic acid bacteria, and more specifically to the species of the Lactobacillus, Leuconostoc and Streptococcus. Examples of the producers of dextrans are to be found in the table below.
Purified dextrans are generally obtained by deproteinization of polysaccharides, which are isolated from the fermentation fluids.
Further purification is obtained by fractionated precipitation with alcohol or ketones. Dextrans which have a well defined molecular weight are obtained by partial hydrolysis.
The structure (such as length of the chain, degree of branching, type of links) of the dextrans are mainly defined by the bacteria subspecies, and less by the family, the genus, or the species. Some of the bacteria produced soluble and insoluble dextrans at the same time.
The basic structure of dextrans are (1-6) linked xcex1-D-glucopyranosyl residues. Sometimes, there are branchings at C-2, C-3, or C-4. Isolated (1-3) linked xcex1-D-glucopyranosyl residues or sequences of these residues can interrupt the (1-6) regions. All of the dextrans are more or less ramified, and the branching very much depends on the subspecies (Jeans A. et al., J. Am. Chem. Soc., 1954, 76, 5041-5052). Most of the branchings are composed of single xcex1-D-glucopyranosyl residues, although branchings have been found with 2-50 monomers. Some branchings are formed by (1-3) linked xcex1-D-glucopyranosyl residues.
Alternane is composed of glucose entities, which are alternately xcex1(1-6)-linked and xcex1(1-3) linked. It is amongst others produced by Leuconostoc mesenteroides NRRL B-1355.
Soluble dextrans are composed of sequences of (1-6) linked xcex1-D-glucopyranosyl residues, on which, at irregular intervals, branchings of single xcex1-D-glucopyranosyl residues are substituted.
Insoluble dextrans are more complex and they often contain more (1-3) linked xcex1-D-glucopyranosyl sequences.
Dextrans are synthesized by dextransucrase (E.C.2.4.1.5). The IUPAC name is sucrose: 1,6-xcex1-D-glucan 6-xcex1-D-glucosyltransferase (IUB, 1984). The enzyme is most frequently extracellular, and is induced by sucrose. The pH-optimum for the Leuconostoc dextransucrase lies between the pH 5.0 and pH 5.5 at the temperature of 29-34xc2x0 C.
A procedure for the production and the isolation of dextransucrase of Leuconostoc mesenteroides is described by Ajongwen N. J. (Biotechnol. Lett., 1993, 9(4), 243-248).
Dextrans can also be synthesized by means of dextrine dextranase (E.C. 2.4.1.2) of for instance Acetobacter capsulatus ATCC 11894 Kazuya Yamamoto (Biosci., Biotech, Biochem. 1993, 57(9), 1450-1453).
The chain length of the dextrans depends on the conditions of fermentation. This means that the presence of acceptors such as maltose will influence molecular weight.
Dextrans form viscous solutions. These solutions show a Newtonian behavior when concentrations  less than 30% w/w for low molecular weight dextrans. Dextrans with a higher molecular weight show a slightly pseudoplastic behavior when concentrations  greater than 1.5% w/w (McCurdy R. D., 1994) There are no single correlations between the viscosity of dextrans solution and its branchings. The viscosity enhancing effect is due to a combination of structure (more or less branched) and molecular weight (Jeanes A. et al., J. Am. Chem. Soc., 1954, 76, 5041-5052).
The present invention is related to a process for obtaining improved structure build-up of baked products comprising the step of incorporating into a dough a sufficient amount of exopolysaccharides, said exopolysaccharides showing in a solution a rise in viscosity (when subjected to a constant stress) with time and showing thereafter the maintain of the achieved viscosity. Preferably, said rise in viscosity is higher than 0.4xc3x9710xe2x88x923 Pas preferably higher than 0.8xc3x9710xe2x88x923 Pas after 5,000 seconds for a 1% solution by weight of exopolysaccharides under stress of 0.5 pa. Therefore, the inventors noticed that said exopolysaccharides surprisingly are capable of a considerable increase of the specific volume of a baked product. Advantageously, said expolysaccharides, preferably dextrans, are obtained from bacteria belonging to the group of lactic acid bacteria. Mainly dextrans with a high molecular weight ( greater than 2xc3x97106 dalton) and few branching seem to have the most marked effect. In many cases, such dextrans also give very viscous solutions. The effect is not merely due to viscosity as such, because xanthan does not have the same effect and still it forms very viscous solutions. Guar also gives viscous solutions and has a bad and limited effect on the bread volume. Slightly ramified dextrans with a low viscosity but with a high molecular weight have also been tested. The positive effect of the dextrans of the leuconostoc mesenteroides subspecies especially the strain LMGP 16878 (hereafter called P-171) is mostly pronounced (p-171). The dextrans are preferably composed of linear chains with a high molecular weight. Dextrans with a high molecular weight and more branchings are less efficient, as proven by the dextrans of Lactobacillus sanfrancisco P-172 and Leuconostoc mesenteroides B512F as described hereafter. Linear dextrans with a low molecular weight are also less efficient. The molecular weight and the degree of branching depend on the subspecies and the conditions of fermentation (sucrose concentration, temperature).
The present invention is also related to new dextrans exceeding 2xc3x97106 dalton and having a branching grade lower than 5%. Preferably, said dextrans are also characterized by the 1H-NMR spectra as represented in the enclosed FIG. 2. Preferably, said dextrans are lyophilized. Another aspect of the present invention is related to a micro-organism producing the dextrans according to the invention and having preferably the deposit number LMGP-16878. A last aspect of the present invention is related the dough and the baked food products comprising the dextrans according to the invention such as bread, xe2x80x9cBelgian pistoletsxe2x80x9d, deep frozen dough, cake, sponge cake, etc.
The subspecies Leuconostoc mesenteroides of the invention was deposited according to the Budapest Treaty in the Belgian Coordinated Collection of Micro-Organisms (BCCM) under the number LMGP-16878.